The present invention relates to motion transmitting devices and, more particularly, to a device for converting bidirectional input motion to single directional output motion. The present invention pertains even more specifically to a linkage assembly for controlling, from a single control member, the engine speed of a vehicle, and the vehicle speed and direction.
Many vehicles, including industrial lift trucks and loaders, are often equipped with a hydrostatic transmission or a torque converter transmission which controls vehicle speed and direction. The transmission provides for infinite variation of the drive ratio between the engine and the drive wheels in both the forward and reverse directions. The drive ratio and the drive direction are controllable by selectively moving a control member away from a central or neutral position. Motion of the control member in one direction from the neutral position progressively increases the drive ratio in the forward drive mode while motion of the control member in the opposite direction from the neutral position progressively increases the drive ratio in the reverse drive mode.
Such vehicles also include an engine speed control device including, for example, a carburetor or a fuel injector, which is controlled to increase engine speed as the drive ratio increases in either the forward or reverse directions. The engine speed control device is itself controlled by a control member, such as an accelerator pedal, which is movable away from a neutral position to increase engine speed.
In some industrial trucks or loaders, the vehicle speed and directional control function on the one hand, and the engine speed control function on the other hand, are accomplished by the same movement of an operator's single control member. A linkage assembly connects, for example, the hydrostatic transmission and carburetor to the single control member to control such a transmission and carburetor. The linkage is capable of shifting a swash plate in the transmission in either of two directions for forward and reverse drive, respectively, in accordance with the corresponding movement of the single control member from the neutral position. Concurrently, the linkage assembly shifts a throttle valve in the carburetor a proportionate amount but always in the same direction regardless of the direction of movement of the control member from the neutral position. The linkage also enables continued movement of the throttle valve in a single direction after the swash plate has reached the limit of travel in either direction. Thus, on movement of the control member in one direction from a neutral position, the linkage assembly causes the transmission to place the vehicle in forward drive at various drive ratios while increasing engine speed. On movement of the control member in the other direction from the neutral position, the linkage assembly causes the transmission to place the vehicle in reverse drive at various drive ratios while also increasing engine speed.
A number of different linkage assemblies have heretofore been used for interconnecting a single operator's control member with both a hydrostatic transmission and a carburetor or fuel injector to perform the above-described functions. However, such assemblies have the disadvantages of being complex and costly. Also, these assemblies are non-compact and, therefore, require more physical space than is desirable.